Devices such as LSIs (Large Scale Integrations) that use a plurality of power supplies, for example, a core power supply, an I/O (Input/Output) power supply, and the like often do not normally operate unless a proper power supply sequence is kept. Accordingly, various power supply control apparatus are devised and put into practical use to control the power supply sequence. A first power supply control apparatus (refer to, for example, Japanese Patent Application Laid-Open No. 2004-180385) and a second power supply control apparatus will be sequentially explained below as examples of conventional power supply control apparatus.
First, the first conventional power supply control apparatus will be explained. FIG. 7 is a view illustrating a configuration of the first conventional power supply control apparatus. As shown in FIG. 7, the first power supply control apparatus 10 has an input supply power source 11, DC-DC converters 12a to 12c, voltage monitoring circuits 13a, 13b, and a load circuit 14.
The input supply power source 11 is a circuit for supplying a voltage to the DC-DC converters 12a to 12c. A plus terminal of the input supply power source 11 is connected to Vin (+) of each of the DC-DC converters 12a to 12c, and a minus terminal of the input supply power source 11 is connected to Vin (−) of each of the DC-DC converters 12a to 12c. A voltage supplied from the input supply power source 11 to the DC-DC converters 12a to 12c is shown by Vin.
Each of the DC-DC converters 12a to 12c is a circuit which has Vin (+), Vin (−), Vout (+), Vout (−) and ON/OFF terminals, and supplies power to the load circuit 14 when it receives power from the input supply power source 11 and the ON/OFF terminal is turned “ON”. In the following explanation, voltages supplied from the DC-DC converters 12a to 12c to the load circuit 14 are shown by Vout 1 to Vout 3.
The voltage monitoring circuit 13a is a circuit which is connected to Vout (+) and Vout (−) of the DC-DC converter 12a and sets the ON/OFF terminal of the DC-DC converter 12b to “ON” when it detects Vout 1 supplied from the DC-DC converter 12a to the load circuit 14.
The voltage monitoring circuit 13b is a circuit which is connected to Vout (+) and Vout (−) of the DC-DC converter 12b and sets the ON/OFF terminal of the DC-DC converter 12c to “ON” when it detects Vout 2 supplied from the DC-DC converter 12b to the load circuit 14.
The load circuit 14 is a circuit for executing various processing making use of the voltages sequentially supplied from the DC-DC converters 12a to 12c. 
Next, operation waveforms of the first power supply control apparatus shown in FIG. 7 will be explained. FIG. 8 is a view illustrating the operation waveforms of the first power supply control apparatus. Note that the ON/OFF terminal of the DC-DC converter 12a is turned “ON”.
When the input supply power source 11 supplies Vin to the DC-DC converters 12a to 12c (refer to Vin of FIG. 8), since the ON/OFF terminal of the DC-DC converter 12a is turned “ON”, Vout 1 is output from the DC-DC converter 12a (refer to Vout 1 of FIG. 8).
When the voltage monitoring circuit 13a detects Vout 1 from the DC-DC converter 12a, the voltage monitoring circuit 13a applies a voltage S1 to the ON/OFF terminal of the DC-DC converter 12b (refer to S1 of FIG. 8), and the ON/OFF terminal of the DC-DC converter 12b is turned “ON”. When the ON/OFF terminal of the DC-DC converter 12b is turned “ON”, the Vout 2 is output from the DC-DC converter 12b (refer to Vout 2 of FIG. 8).
When the voltage monitoring circuit 13b detects Vout 2 from the DC-DC converter 12b, the voltage monitoring circuit 13b applies a voltage S2 to the ON/OFF terminal of the DC-DC converter 12c (refer to S2 of FIG. 8), and the ON/OFF terminal of the DC-DC converter 12c is turned “ON”. When the ON/OFF terminal of the DC-DC converter 12c is turned “ON”, Vout 3 is output from the DC-DC converter 12c (refer to Vout 3 of FIG. 8).
As described above, in the first power supply control apparatus 10, when, for example, powers are supplied to the load circuit 14 in the sequence of the DC-DC converters 12a to 12c, the DC-DC converters 12a to 12c are sequentially connected in this power supply sequence, and the voltage monitoring circuits 13a, 13b turn “ON” and “OFF” the ON/OFF terminals of the DC-DC converters 12b, 12c. 
Next, the second conventional power supply control apparatus will be explained. FIG. 9 is a view illustrating a configuration of the second conventional power supply control apparatus. As shown in FIG. 9, the second power supply control apparatus 20 has an input supply power source 21, DC-DC converters 22a to 22c, a delay signal circuit 23, and a load circuit 24.
The input supply power source 21 is a circuit for supplying a voltage to the DC-DC converters 22a to 22c. A plus terminal of the input supply power source 21 is connected to Vin (+) of each of the DC-DC converters 22a to 22c, and a minus terminal of the input supply power source 21 is connected to Vin (−) of each of the DC-DC converters 22a to 22c. A voltage supplied from the input supply power source 21 to the DC-DC converters 22a to 22c is shown by Vin.
Each of the DC-DC converters 22a to 22c is a circuit which has Vin (+), Vin (−), Vout (+), Vout (−) and ON/OFF terminals and supplies power to the load circuit 24 when it receives power from the input supply power source 21 and the ON/OFF terminal is turned “ON”. In the following explanation, voltages supplied from the DC-DC converters 22a to 22c to the load circuit 24 are shown by Vout 1 to Vout 3.
The delay signal circuit 23 is a circuit for outputting control signals to the DC-DC converters 22a to 22c according to a power supply sequence and sequentially turning “ON” the ON/OFF terminals of the DC-DC converters 22a to 22c. When, for example, voltages are sequentially supplied to the load circuit 24 in the order of Vout 1 to Vout 3, the delay signal circuit 23 inputs control signals S1 to S3 in the order of the DC-DC converters 22a to 22c. 
The load circuit 24 is a circuit for executing various processing making use of the voltages sequentially supplied from the DC-DC converters 22a to 22c. 
Next, operation waveforms of the second power supply control apparatus 20 shown in FIG. 9 will be explained. FIG. 10 is a view illustrating the operation waveforms of the second power supply control apparatus 20. Note that a case where voltages are supplied to the load circuit 24 in the order of Vout 1 to Vout 3 will be explained here as an example.
The input supply power source 21 supplies Vin to the DC-DC converters 22a to 22c (refer to Vin of FIG. 10). When the delay signal circuit 23 outputs a control signal S1 to the DC-DC converter 22a (refer to S1 of FIG. 10), the ON/OFF terminal of the DC-DC converter 22a is turned “ON”, and Vout 1 is output from the DC-DC converter 22a (refer to Vout 1 of FIG. 10).
When the delay signal circuit 23 outputs a control signal S2 to the DC-DC converter 22b at a predetermined time interval after it outputs the control signal S1 to the DC-DC converter 22a (refer to S2 of FIG. 10), the ON/OFF terminal of the DC-DC converter 22b is turned “ON”, and Vout 2 is output from the DC-DC converter 22b (refer to Vout 2 of FIG. 10).
When the delay signal circuit 23 outputs a control signal S3 to the DC-DC converter 22c at a predetermined time interval after it outputs the control signal S2 to the DC-DC converter 22b (refer to S3 of FIG. 10), the ON/OFF terminal of the DC-DC converter 22c is turned “ON”, and Vout 3 is output from the DC-DC converter 22c (refer to Vout 3 of FIG. 10).
In the second power supply control apparatus, when, for example, powers are supplied to the load circuit 24 in the order of the DC-DC converters 22a to 22c as described above, the delay signal circuit 23 sequentially inputs the control signals S1 to S3 to the ON/OFF terminals of the DC-DC converters 22a to 22c in this sequence.
However, when the first power supply control apparatus 10 is assembled to an actual device and a power supply sequence is controlled, it is preferable to control a start-up sequence between elements in addition to the power supply sequence to the load circuit. FIG. 11 is a view illustrating an example where the first power supply control apparatus 10 is assembled to the actual device. As shown in FIG. 11, since it is preferable to control many DC-DC converters to control the power supply sequence to a plurality of LSIs, a start-up sequence becomes complex. Further, in the first power supply control apparatus 10, signal wires is connected to each other between the DC-DC converters according to the start-up sequence and thus many signal wires are wired in a complex fashion. Since various controls are executed on a highly dense wiring substrate in addition to a control of a power supply sequence, a space for wiring many wires does not remain in the wiring substrate unlike the first power supply control apparatus 10.
Further, once the first power supply control apparatus 10 is assembled to the actual device, it is very difficult to change a start-up sequence because destinations of connections of signal wires may be changed. Note that there is a possibility of avoiding difficulty of changing the start-up sequence by assembling the second power supply control apparatus 20 to an actual device. However, even if the second power supply control apparatus 20 is used, since different signal lines are connected from the delay signal circuit 23 to the DC-DC converters, a problem of pressing a region on a wiring substrate may not be overcome as in the first power supply control apparatus 10.